Method and system of destruction of volatile compounds in wastewater

ABSTRACT

The invention proposes a method of destruction of volatile organic and inorganic compounds in wastewater, this method includes following stages: stripping the aforementioned volatile compounds in a stripping-chemisorption column; preliminary heating the gaseous medium containing these volatile compounds in a first heat regenerator; thermal, flare or thermo-catalytic oxidation of the volatile compounds in circulating gaseous medium; cooling the gaseous medium in a second heat regenerator; chemisorption of acidic gases from the gaseous medium in the stripping-chemisorption column with stripping at the same time additional amount of the volatile compounds from the wastewater. After specific period, direction of the gaseous medium flow is alternated. The proposed method can be executed at elevated temperature. The invention includes as well systems realizing the proposed method.

CROSS-REFERENCE APPLICATION

Not Applicable

FEDERALLY SPONSORED RESEARCH OF DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

The problem of treatment of wastewater contaminated with volatileorganic or inorganic compounds becomes very pressing for many facilitiesand for many branches of industry. In some cases, volatile organic andinorganic compounds present a major contributor to overall pollution ina facility.

There are different methods of volatile organic and inorganic compoundscontrol in wastewater.

Detailed review of these methods is presented in the article: Victor H.Edwards “VOC-Control Options During Wastewater Treatment” CHEMICALENGINEERING, September 2000, pp. 105÷108.

According to this article, all methods of control of volatile organicand inorganic compounds in wastewater can be classified under two maintypes: 1) with transfer of volatile organic and inorganic compounds fromwastewater into vapor phase by distillation, air stripping, steamstripping, inert-gas stripping, fuel-gas stripping, vacuum distillationand vacuum stripping; 2) with transfer of volatile organic and inorganiccompounds into a liquid or solid phase: solvent extraction, liquid ionexchange, reverse osmosis, adsorption, ion exchange and precipitation.

Each aforementioned method is distinguished by its advantages anddrawbacks.

In the case of application of air stripping related to the first group,this method should be combined with an additional method for treatingair laden with volatile organic and inorganic compounds. There areseveral physicochemical methods of such additional treatment: flare,feed to a furnace or boiler, feed in a thermal or catalytic incinerator,condensation, cryogenic condensation, adsorption using activated carbon,alumina or zeolites.

Each of these additional methods has in turn several advantages anddisadvantage related to its cost, efficiency, reliability and safety. Asit is known from technical literature (see, for example, “THERMAL ANDTHERMO-CATALYTIC TREATMENT OF WASTE GASES” Naukova Dumka, 1984, pp.17÷22 (in Russian)), thermal method of oxidation of waste gases requiresabout of 26÷45 kg of liquid fuel per 1000 m³ of waste gases and thethermo-catalytic method—15÷25 kg of liquid fuel correspondingly. It isclear, that higher concentration of volatile organic and inorganiccompounds in the volatile organic and inorganic compounds-laden airafter the air stripping process causes diminishment of a liquid orgaseous fuel required for thermal or thermo-catalytic oxidation ofvolatile organic and inorganic compounds presented in the wastewater.

In order to achieve higher concentration of volatile organic andinorganic compounds in the volatile organic and inorganiccompounds-laden air it is possible to perform the air stripping processwith a stage of previous heating wastewater in a heat exchanging unit,it allows achieving higher concentration of volatile organic andinorganic compounds in air after stripping process and, on the otherhand, to treat wastewater containing volatile organic compounds withrelatively high temperature of boiling at the atmospheric pressure.

In addition, the rate of stripping at elevated temperature issubstantially higher, i.e. for the same size of an air-stripping tower,it is possible to treat greater amount of wastewater in the same period.

However, the common process of air stripping at elevated temperature ischaracterized by great heat losses at the expense of enhanced waterevaporation into the volatile organic and inorganic compounds-laden air.As a result, energy cost for wastewater treatment by air stripping atelevated temperatures is very high.

BRIEF SUMMARY OF THE INVENTION

A proposed technical solution is based on the stripping-chemisorptionprocess performed mainly at elevated temperature.

A system of treatment of volatile organic and inorganic compoundscontained in wastewater comprises some main units: a tank filled withthe wastewater; two stripping-chemisorption columns installed on thetank through two connecting branches; two fans or blowers causingcirculation of the gaseous medium through the system with periodicalalternation of circulation direction; two heat regenerators that operatein opposite phases with periodical alternation their modes; a unit ofthermal, flare or thermo-catalytic oxidation of volatile organic andinorganic substances contained in the circulating gaseous medium.

The wastewater in tank has alkali reaction (pH>7); it can be achieved byaddition of alkali substances into the wastewater. This serves forchemisorption of acidic gases obtained by thermal, flare orthermo-catalytic oxidation of the organic or/and inorganic compoundsevaporated previously in the stripping-chemisorption columns. The systemis provided with an inlet connection for oxygen delivery and with anoutlet connection for blowing out the system, especially, at the initialstage of its operation.

The unit of thermal, flare or thereto-catalytic oxidation (incineration)of volatile organic and inorganic compounds contained in the gaseousmedium can be designed in flare, thermal or thermo-catalytic forms.

A circulation pump associated with the tank performs supply of thewastewater from this tank to the upper section(s) of thestripping-chemisorption column(s), which are installed on the tankthrough the aforementioned connecting branches.

The upper edges of the stripping-chemisorption columns are joined inturn with the bottoms of fixed packed beds (heat regenerators) servingfor periodic accumulation of heat from the gaseous medium after flare,thermal or thermo-catalytic oxidation of volatile organic and inorganiccompounds contained in this gaseous medium and its preheating beforetheir flare, thermal or thermo-catalytic oxidation. The upper edges ofthese fixed packed beds (heat regenerators) are communicating with aunit of flare, thermal or thermo-catalytic oxidation.

Besides, in the case of thermo-catalytic oxidation, there are twomodules of ultimate heating situated between the unit of flare, thermalor thereto-catalytic oxidation and the heat regenerators.

Both connecting branches, which are installed on the tank, are joined bytwo parallel channels, which are provided with demisters and shuttersinstalled in their extreme sections; the fans are installed in thesechannels and actuated alternatively in accordance with modes of the heatregenerators, they cause circulation of the gaseous medium through theentire system. The basic processes in the entire system include:stripping-chemisorption by the stripping-chemisorption columns,preheating the gaseous medium by, one of the heat regenerators, thermal,flare or thermo-catalytic oxidation in the thermal or thermo-catalyticoxidation unit, and heat accumulation in the other heat regenerator.

There are two tubular branches inserting from the lower edges of theconnecting branches into the wastewater in the tank, it allows toprevent bypass flow of the gaseous medium via the upper space of thetank (if this tank is not filled completely with the wastewater).

In the case of thermal oxidation of volatile organic and inorganiccompounds in the circulating gaseous medium, it is possible to designthe heat regenerators and the thermal oxidation unit as a combinedmodule in the form of a tube from refractory material with an internalpacking; the middle section of the tube is provided with a heating means(electrical or flare) and the extreme sections of this refractory tubewith the internal packing serve as the heat regenerators.

In another version, the fans are installed between thestripping-chemisorption column and the heat regenerators. In thisversion, the stripping-chemisorption columns are installed directly onthe tank with wastewater (without application of the connectingbranches) and the aforementioned tubular branches inserted in the spaceof the wastewater tank are not applied. The upper internal section ofthe tank, which is not filled with the wastewater, serves in this casefor circulation of the gaseous medium and the aforementioned parallelchannels are not applied as well.

The tank can be provided with a build-in or external heat-exchangingmodule.

In addition, the proposed system is provided with proper controlequipment and valves.

The proposed system, when it is designed for thermo-catalytic oxidationof volatile organic and inorganic compounds, operates in the followingmanner:

the tank should be filled with wastewater contaminated with volatileorganic and inorganic compounds;

if it is necessary, the wastewater temperature in the tanks isestablished at a level, which is required for rapid and safety strippingvolatile organic and inorganic compounds with their following oxidationin gaseous medium;

alkalinity of this wastewater in the tanks can be established previouslyor in the process of oxidation of volatile organic and inorganiccompounds at a level, which ensures complete neutralization andchemisorption of acidic gases obtained as the result of oxidation ofthese volatile organic and inorganic compounds;

the circulation pump is actuated and it supplies the wastewater from thetank into one or both stripping-chemisorption columns; if it isnecessary, the wastewater temperature in this tank is established by itsheat-exchanging module;

at the same time, one of fans is actuated in such a way, that it causescirculation of the gaseous medium in the entire system when this gaseousmedium flows co-currently or counter-currently regarding the wastewaterflow in the operating stripping-chemisorption columns;

after preheating the gaseous medium in one fixed packed bed (heatregenerator) and its ultimate heating by the electrical heater in themodule of ultimate heating the gaseous medium passes through thecatalytic bed, and volatile organic and inorganic compounds contained inthe gaseous medium are oxidized by oxygen presented in the gaseousmedium;

then the gaseous medium is pre-cooled in the opposite heat regenerator;

oxygen or air is steadily supplied into the gaseous medium in accordancewith amount of oxygen which is run out for oxidation of volatile organicand inorganic compounds in the gaseous medium.

Finally cooling is performed in the following operatingstripping-chemisorption column(s) itself. Besides, this operatingstripping-chemisorption column provides additional evaporated portionsof volatile organic and inorganic compounds into the circulating gaseousmedium, causes absorption of the oxidation products in the wastewaterand regulates the water vapors' content in the gaseous medium.

As the average temperature in the heat regenerator, which serves at thispoint for cooling the gaseous medium after the unit of thermo-catalyticoxidation, is elevated up to a certain level, operation of the fans isalternated, i.e. the first fan will be in its idle state and the secondfan begins to circulate the gaseous medium through the system inopposite direction. As this takes place, the second module of ultimateheating is actuated instead of the first module.

After getting sufficiently low concentration of volatile organic andinorganic compounds in the wastewater, the process is finished and thewastewater is discharged from the tank.

In order to indicate temperature change and volatile organic andinorganic compounds' concentration in the wastewater or in the gaseousmedium, the system is provided with a proper monitoring unit.

It is possible to simplify the system described above by introduction offour shutoff dampers. In this case, there is only onestripping-chemisorption column. Closing and opening the diagonallypositioned pairs of the shutoff dampers can alternate direction of thegaseous medium flow via the aforementioned fixed packed beds.

Two modules of ultimate heating and one module of thermo-catalyticoxidation are positioned between these fixed packed beds (heatregenerators), the modules of ultimate heating are energizedalternatively in accordance with direction of the gaseous stream. Thisversion gives possibility to apply only one fan.

If wastewater contains volatile organic acid, for example—acetic acid,than stripping and chemosorption processes should be performed indifferent columns connected in series, because high alkalinity maysignificantly diminish volatility of this acid. In this casechemisorption of the gases obtained by thermo-oxidation orthermo-catalytic oxidation is performed in a separate column by alkalinesolution.

The stripping-chemisorption columns can be of the spray or packed types.

In the case of flare or thermal oxidation, the modules of ultimateheating are not applied.

The heat exchanging module(s) of the tank(s) allows to changetemperature of the wastewater in the tank in order to establishsufficiently high rate of evaporation of volatile organic and inorganiccompounds and, on the other hand, to prevent danger of explosion of thegaseous medium.

In the case of flare or thermal oxidation of volatile organic andinorganic compound-laden gaseous medium there is only one module ofultimate heating (or incineration) and oxidation is performed in thismodule.

The proposed design of the stripping-chemisorption-oxidation systemallows diminishing consumption of electrical energy, liquid or gaseousfuel for flare, thermal or thermo-catalytic oxidation of volatileorganic and inorganic compounds contained in wastewater. Thisdiminishment can be estimated by a factor of 2÷4.

In the case, when the wastewater contains high concentration of volatileorganic and inorganic compounds, it is possible to diminish further thisenergy expenditure at the cost of the heat released in the process ofvolatile organic and inorganic compound oxidation.

In the batch version of the process, the temperature of the wastewateris changed during the process of stripping-chemisorption in such a way,that concentration of explosive volatile organic and inorganic compoundsin the gaseous medium in the system is significantly lower than adangerous level, which can cause explosion. In addition, it is possibleto cool the wastewater in the tanks at the early stage of oxidation inorder to prevent danger of explosion (in the case of high initialconcentration of volatile organic and inorganic compounds in thewastewater).

In the continuous version of the process, there are somestripping-chemisorption-oxidation sub-units, which are arranged in lineand the temperature of the wastewater is gradually elevated in thedirection from the first stripping-chemisorption-oxidation sub-unit tothe latter. In such a way, concentration of volatile organic andinorganic compounds in the gaseous medium of eachstripping-chemisorption-oxidation sub-unit is lower than the dangerouslevel because gradually diminishment of volatile organic and inorganiccompound concentration in the stripping-chemisorption-oxidationsub-units according to downstream of the wastewater.

The main area of application of the proposed systems is treatment ofwastewaters of different facilities.

However, these systems can be used as well for treatment of groundwaterin the case, when this groundwater has high level of contamination byvolatile organic and inorganic compounds (for example, in the case ofspillage at a facility).

In addition the proposed system can be used for incineration ofwater-insoluble organic liquids, for example, waste PCB. In this case,the tank(s) of the system is filled with the waste organic liquid andaqueous alkali solution in a required proportion. The tank is providedwith a mixer, which generates emulsion of both components (the aqueousalkali solution and the organic liquid), this emulsion is supplied bythe circulation pump to the stripping-chemisorption column.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a general scheme of a system for destruction of volatileorganic and inorganic compounds contained in wastewater, this schemeincludes a tank with a circulating pump and two stripping-chemisorptioncolumns; oxidation of volatile organic and inorganic compounds isperformed by a thermo-catalytic unit.

FIG. 2 is a general scheme of a system for destruction of volatileorganic and inorganic compounds contained in wastewater, this systemincludes a tank with a circulating pump and two stripping-chemisorptioncolumns, oxidation of volatile organic and inorganic compounds isperformed by a thermal unit.

FIG. 3 is a general scheme of a system for destruction of volatileorganic and inorganic compounds contained in wastewater, this system isbased on thermal oxidation of volatile organic and inorganic compounds;the heat regenerators and the thermal oxidation unit are designed as onecombined module.

FIG. 4 is a general scheme of a system for destruction of volatileorganic and inorganic compounds contained in wastewater bythermo-catalytic oxidation; this system comprises onestripping-chemisorption column and one fan.

FIG. 5 is a general scheme of a system for destruction of organic acidscontained in a wastewater.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a general scheme of a batch system for destruction ofvolatile organic and inorganic compounds contained in wastewater bythermo-catalytic oxidation.

This scheme includes tank 101 filled with wastewater 102 in such a way,that there is a free upper space intended for circulation of the gaseousmedium. The tank comprises: outlet connections 104 and 103, an inletconnection 105, flanges 106 and 107 for installation ofstripping-chemisorption columns 110 and 112, a built-in heat exchangingmodule 109. This heat exchanging module is installed on an additionalflange 111. The stripping-chemisorption columns 110 and 112 comprisepackings 113 and 114, distributors 115 and 131, demisters 117 and 116. Acirculation pump 108 performs circulation the wastewater via thestripping-chemisorption columns 110 and 112. Fans 118 and 119 areinstalled on the upper flanges of the stripping-chemisorption columns110 and 112.

In addition, there are two heat regenerators 120 and 121 installed bytheir lower flanges on fans 118 and 119. The heat regenerator 120 isprovided with an inlet connection 129 for oxygen delivery and the heatregenerator 121—with an outlet connection 130 for purging the entiresystem.

The heat regenerator 120 is filled with packing 122, and heatregenerator 121—with packing 123.

Module 124 for thermo-catalytic oxidation consists of two sub-modules125 and 126 of ultimate heating, and a catalytic packed bed 127.

The heat regenerators 120, 121 and module 124 are provided with athermal insulation 128.

FIG. 2 shows a general scheme of a batch system for destruction ofvolatile organic and inorganic compounds contained in wastewater bythermal oxidation. This scheme includes tank 201 filled with wastewater202. Tank 201 is provided with an inlet connection 204, outletconnections 203 and 204, flanges 206 and 207 for installation of twoconnecting branches 212 and 213. Each connecting branch is provided withtwo lateral tees.

In addition, tank 201 is provided with a built-in heat exchanging module208. Tubular branches 209 and 210 are installed on flanges 206 and 207.They are immersed into the wastewater; it prevents bypass flow of thegaseous medium through the upper space of the tank.

The connecting branch 212 is provided with an inlet connection 240 foroxygen delivery, and the connecting branch 213—with an outlet connection241 for purging the entire system. The lateral tees of the connectingbranches are joined by two joints; there are demisters 214 and 215, fans217 and 219, back draft shutters 216 and 218, which are installed inthese joints.

The upper flanges of the connecting branches 212 and 213 serve forinstallation of two stripping-chemisorption columns 220 and 221 withsupporting grids 222 and 223, and packings 224 and 225.

In addition, there are distributors 226, 229 and demisters 228, 227installed in the stripping-chemisorption columns. Pump 211 performssupply of the wastewater into the stripping-chemisorption columns.

The upper flanges of the stripping-chemisorption columns serve forinstallation of their associated heat regenerators 233, 232 withpackings 238 and 242. This installation is performed through two bellowjoints 222 and 223.

The low sections of the heat regenerators consist off metal branches 234and 235; refractory tubes 236 and 237 are inserted into these metalbranches. These refractory tubes are joined by refractory elbows 244 and245 with module 243 of thermal oxidation; this module comprises arefractory tube 246 and an internal electrical heater 243.

The heat regenerators 232, 233 and module 243 of thermal oxidation areprovided with a thermal insulation 239.

FIG. 3 shows a general scheme of a batch system for destruction ofvolatile organic and inorganic compounds contained in wastewater a plantof volatile organic and inorganic compound-control in wastewater, thisscheme is based on thermal oxidation of volatile organic and inorganiccompounds; the heat regenerators and the unit of thermal oxidation aredesigned as one combined module of tubular form.

This scheme includes tank 301 filled with wastewater 302. Tank 301 isprovided with an inlet connection 304, outlet connections 303 and 307,flanges 306 and 308 for installation two connecting branches 313 and315. Each connecting branch is provided with two lateral tees.

In addition, tank 301 is provided with a built-in heat exchanging module305. Tubular branches 337 and 338 are installed on flanges 306 and 308.They are immersed into the wastewater, it prevents bypass flow of thegaseous medium through the upper space of the tank.

The connecting branch 315 is provided with an inlet connection 311 foroxygen delivery, and the connecting branch 313—with an outlet connection309 for purging the entire system. The lateral tees of the connectingbranches are joined by two joints; there are demisters 316 and 317, fans312 and 320, back draft shutters 314 and 321, which are installed inthese joints.

The upper flanges of the connecting branches 313 and 315 serve forinstallation of two stripping-chemisorption columns 318 and 319 withpackings 323 and 322.

In addition, there are distributors 325, 327 and demisters 326, 328installed in the stripping-chemisorption columns. Pump 310 performssupply of the wastewater into the stripping-chemisorption columns.

The upper flange of the stripping-chemisorption column 315 serves forinstallation a bellow joint 331, which in turn serves for installationof a combined module 324 of heat regeneration—thermal oxidation.

The low section of the combined module 324 consists off a metal branch330 with supporting grid 329; a refractory tube 336 is inserted intothis metal branch. The refractory tube 336 is filled with packing 332.

The middle section of the refractory tube 336 is provided with anexternal electrical heater 333, and its lower and upper sections serveas heat regenerators. The refractory tube 336 is provided with a thermalinsulation 335.

A gas duct 334 communicates the upper section of the combined module 324with the upper flange of the stripping-chemisorption column 319.

FIG. 4 shows a general scheme of a plant of volatile organic andinorganic compound-control in wastewater by thermo-catalytic oxidationwith one stripping-chemisorption column.

This scheme includes tank 401 filled with wastewater 402. The tankcomprises: outlet connections 404 and 403, an inlet connection 405,flange 410 and a built-in heat exchanging module 406. Flange 410 servesfor installation of a connecting branch 409 with a lateral tee.

A stripping-chemisorption column 416 is installed on the upper flange ofthe connecting branch 409, this column comprises packing 411 anddistributor 412.

A circulation pump 407 performs circulation the wastewater via thestripping-chemisorption column 416.

The lateral tee of the connecting branch 409 is joined with the proximaledge of a gas duct 420; the distal edge of this gas duct is joined withthe upper flange of the stripping-chemisorption column 416. In such away, these units—the gas duct 420, the stripping-chemisorption column416 and the connecting branch 409—present a closed loop for circulationof gaseous medium. The proximal section of the gas duct is provided withdemister 413 and fan 414.

There is a first additional gas duct 421, which communicates theproximal and distal sections of the gas duct 420. A heat regenerator419, module 426 of sub-module 426 of ultimate heating, module 417 ofthermo-catalytic oxidation, sub-module 418 of ultimate heating, and aheat regenerator 429 are installed in-line on a second additional gasduct 430 communicating the first additional gas duct 421 with the gasduct 420.

Two pair of dampers 431, 425 and 423, 422 are installed on the gas duct420 and the first additional gas duct 421 from both sides with respectto the second additional gas duct 430. Alternative shutting and openingthe diagonally situated dampers gives possibility to alternateperiodically direction of the gaseous medium flow via the aforementionedsequence of the modules and sub-modules installed on the secondadditional gas duct.

FIG. 5 shows a general scheme of a system for destruction of organicacids contained in a wastewater.

This scheme includes tank 501 filled with wastewater 502. The tankcomprises: outlet connections 504 and 503, an inlet connection 505,flange 510 and a built-in heat exchanging module 506. Flange 510 servesfor installation of a connecting branch 509 with a lateral tee.

A stripping column 516 is installed on the upper flange of theconnecting branch 509, this column comprises packing 511 and distributor512.

A circulation pump 507 performs circulation the wastewater via thestripping column 516. There is a second tank 513 filled with alkalinesolution 514. The tank comprises: outlet connections 517 and 518, aninlet connection 519, flange 520 and a built-in heat-exchanging module521. Flange 520 serves for installation of a connecting branch 522 witha lateral tee.

A chemisorption column 523 is installed on the upper flange of theconnecting branch 522, this column, comprises packing 524 anddistributor 525.

A circulation pump 526 performs circulation the alkaline solution viathe chemisorption column 523.

The lateral tee of the connecting branch 509 is connected with thelateral tee of the connecting branch 522 by a gas duct 527.

The inlet flange of fan 528 is installed on the upper flange of thestripping column 516.

The upper flange of the chemisorption column 523 and the outlet flangeof fan 528 are communicated by a gas duct 529 which is branched in twoparallel gas ducts 530 and 531. The parallel gas ducts include twoT-pieces 532 and 533. The central branches of these T-pieces arecommunicated via a gas duct 534, which incorporates a first heatregenerating bed 535, an electrical heater 536 and a second heatregenerating bed 537; these units are positioned sequentially.

The system is provided with an inlet connection 508 for supply of oxygenand/or other gases into the gaseous circuit of this system, and with anoutlet connection 515 for blow-out of the excessive gases from thesystem.

Two pairs of dampers 538, 539 and 540, 541 are installed on the gasducts 530 and 531 from the both sides of the central branches ofT-pieces 532 and 533.

Alternative shutting and opening the diagonally situated dampers givespossibility to alternate periodically direction of the gaseous mediumflow via the aforementioned sequence of the heat regenerating beds andthe electrical heater.

1-16. (canceled)
 17. A system for processing water contaminated withvolatile compounds, comprising: a stripping unit including a first inletfor contaminated water, a second inlet for a circulating gaseous medium,and an outlet; wherein the stripping unit is operative to strip volatilecompounds from the contaminated water and into said circulating gaseousmedium, and for extraction of oxidation products from said circulatinggaseous medium; an oxidation unit having an inlet coupled to saidstripping unit outlet, to oxidize the volatile compounds in saidcirculating gaseous medium, and to form oxidation products in saidcirculating gaseous medium; an outlet from the oxidation unit for theoxidation product-carrying gaseous medium coupled to the second inlet ofsaid stripping unit; and a heat regeneration system to preheat saidvolatile compound-containing circulating gaseous medium entering saidoxidation unit from said stripping unit, and to cool the oxidationproduct-carrying gaseous medium exiting the oxidation unit.
 18. A systemaccording to claim 17, wherein said heat regeneration system comprises:a first and a second heat exchange unit and a heat flow reversal unit,wherein the heat flow reversal unit is operative to change a directionof heat flow from a first state in which the first heat exchange unitcools the circulating oxidation product-carrying gaseous medium exitingthe oxidation unit and the second heat exchange unit preheats thevolatile compound-carrying circulating gaseous medium entering saidoxidation unit, to a second state in which the second heat exchange unitcools the oxidation product-carrying gaseous medium exiting theoxidation unit and the first heat exchange unit preheats the oxidationproduct-carrying circulating gaseous medium entering said oxidationunit.
 19. A system according to claim 18, wherein said heat flowreversal unit reverses the flow direction of said circulating gaseousmedium.
 20. A system according to claim 19, wherein the heat flowreversal unit includes a blower.
 21. A system according to claim 19,wherein the heat flow reversal unit includes a system of shutters.
 22. Asystem according to claim 18, wherein said heat flow reversal unit isresponsive to an average temperature in the one of said first or saidsecond heat exchange units then being used for cooling said circulatinggaseous medium exiting said oxidation means reaching a certain level.23. A system according to claim 17, wherein said oxidation unit is athermal oxidation unit.
 24. A system according to claim 17, wherein saidoxidation unit is a flare oxidation unit.
 25. A system according toclaim 17, wherein said oxidation unit is a thermo-catalytic oxidationunit.
 26. A system according to claim 17, further comprising a heatingunit operative to heat the wastewater before entry thereof into saidstripping unit.
 27. A system according to claim 17, further comprisingan inlet for adding an additional gas to said volatile compound-carryinggaseous medium entering said oxidation unit from said stripping unit,said additional gas inlet being so located that the additional gas ispreheated together with said volatile compound-carrying gaseous mediumentering said oxidation unit.
 28. A system according to claim 17,wherein the stripping unit includes a chemisorption bed.
 29. A method ofprocessing water contaminated with volatile organic and inorganiccompounds, the method comprising: delivering the contaminated water anda circulating gaseous medium to a stripping unit; stripping the volatilecompounds from the contaminated water and into the circulating gaseousmedium; oxidizing the volatile compounds in said circulating gaseousmedium, the resulting oxidation products being carried in saidcirculating gaseous medium; preheating said circulating gaseous mediumbefore oxidation of the volatile compounds; cooling said oxidationproduct-carrying circulating gaseous medium, said preheating and coolingbeing performed in a heat regeneration system; and removing saidoxidation products carried in said circulating gaseous medium in saidstripping unit.
 30. The method of claim 29, wherein the heatregeneration system includes a first and a second heat exchange unit,and wherein the method further includes reversing a direction of heatflow from a first state in which the first heat exchange unit cools theoxidation product-carrying circulating gaseous medium, and the secondheat exchange unit preheats the circulating gaseous medium beforeoxidation, to a second state in which the second heat exchange unitcools the oxidation product-carrying circulating gaseous medium, and thefirst heat exchange unit preheats the volatile compound-containingcirculating gaseous medium before oxidation.
 31. A method according toclaim 30, wherein the direction of said heat flow is reversed byreversing the flow direction of said circulating gaseous medium.
 32. Amethod according to claim 30, wherein the direction of said heat flow isreversed by a blower.
 33. A method according to claim 30, wherein thedirection of said heat flow is reversed by a system of shutters.
 34. Themethod of claim 30, wherein the direction of said heat flow is reversedwhen average temperature is elevated up to a certain level in said firstor in said second heat exchange unit being used for cooling saidoxidation product-carrying circulating gaseous medium.
 35. A methodaccording to claim 29 further comprising adding an additional gas intosaid volatile compound-carrying gaseous medium before oxidation, saidadditional gas being added at a location such that said additional gasis preheated together with said volatile compound-carrying gaseousmedium.
 36. A method according to claim 35, wherein said additional gasincludes oxygen.
 37. The method of claim 35, wherein the amount of saidadditional gas added into said circulating gaseous medium is determinedin accordance with an amount of oxygen consumed by said oxidation.
 38. Amethod according to claim 29, wherein oxidation products are removedfrom said circulating gaseous medium by chemisorption.
 39. A methodaccording to claim 38, wherein said chemisorption is performed in saidstripping unit.
 40. A method according to claim 29, wherein saidoxidation is performed by thermal oxidation.
 41. A method according toclaim 29, wherein said oxidation is performed by flare oxidation.
 42. Amethod according to claim 29, wherein said oxidation is performed bythermo-catalytic oxidation.
 43. A method according to claim 29, furthercomprising measuring a concentration of the volatile compounds in saidcontaminated water or in said circulating gaseous medium afterstripping, and/or measuring temperatures in different locations in saidcirculating gaseous medium.
 44. A method according to claim 29, furthercomprising changing a temperature of the contaminated water beforestripping.
 45. A method according to claim 44, wherein the temperatureof the contaminated water is changed to achieve a desired rate ofevaporation of the volatile compounds and, to prevent danger ofexplosion of said circulating gaseous medium.
 46. A method according toclaim 43, wherein the temperature of the contaminated water is changedto maintain a concentration of the volatile compounds in saidcirculating gaseous medium significantly lower than a dangerous levelwhich can cause explosion of said circulating gaseous medium.
 47. Amethod according to claim 29, wherein said contaminated water isdelivered to the stripping unit in a continuous stream, and whereinstripping, oxidation, and chemisorption are performed in a plurality ofprocessing subunits, each comprised of a stripping unit, an oxidationunit and a chemisorption unit arranged in series.
 48. A method accordingto claim 47, wherein a temperature of said contaminated water isgradually elevated in a direction starting from first said processingsub-units to maintain a concentration of volatile compounds in thegaseous medium in processing sub-unit lower than a dangerous level. 49.A method according to claim 29, wherein said contaminated water isprocessed in batches.